Waste sulphite liquor recovery



July 30, 1957 H. o. GODDARD WASTE SULP'HITE LIQUOR RECOVERY' NvEN-roR /Hgro/d fgycdddld TTORNEY July 30, 1957 H. o. GODDARD WASTE SULPHITE LIQUOR RECOVERY .Nam

July 30, 1957 H. o. GODDARD WASTE SULPHITE LIQUOR RECOVERY 5 Sheets-Sheet Original Filed April 2, 1949 July 30, 1957 H. o. GODDARD WASTE SULPHITE LIQuoR RECOVERY 5 Sheets-Sheet 4 Original Filed April 2. 1949 NQ @hv mmmjZQD 20m... :(mhwl.

H. o. GoDDARD WASTE SULPHITE LIQUOE RECOVERY July 30, 1957 5 Sheets-Sheet 5 Original Filed April 2 mbv ' INVEN'rol; Haro/ O. Goddard United States Patent M' Original application April 2, 1949, Serial No. 85,116, now

Patent No. 2,676,883, dated April 27, 1954. Divided and this application March 25, 1954, Serial No. 418,725

This invention relates to the recovery of useful products from waste sulphite liquor discharged by sulphite pulp plants.

The present application is a division of application Serial No. 85,116, led April 2, 1949, now Patent No. 2,676,883.

Heretofore, numerous products have been recovered from waste sulphite liquor. For example, the sugars therein have been recovered and used in the production of alcohol. Sulphur dioxide gas and sulphites have been recovered from said liquor. Waste sulphite liquor has also been concentrated or dried and the liquor in concentrated or dried form has been burned. While prior recovery methods of which I am aware 'have been to some degree successful in accomplishing their purposes, they have not been economic in their functioning nor have they been trouble-free in their operation.

The present invention provides a method of and apparatus for the recovery of useful products from waste sulphite liquor in which said products are economically recovered.

A method of and apparatus for producing a finely divided dried solid fuel useful, for example, as a fuel in a steam generator is also provided by the present invention. p

In accordance with the present invention, steam for use in the operation of a sulphite pulp plant is generated to a pressure higher than that required for the operation of the digesters, paper machine dryers, or other steam consumers in said plant, and at the higher pressure is used to concentrate and to dry the waste sulphite liquor into a form which is usable as a fuel in a steam generator. The dry solids from the concentrated and dried waste sulphite liquor, which contain approximately 8,000 B. t. u. per pound of dry solids, are produced, in accordance with the present invention, in a finely divided state and may readily be substituted for pulverized coal to fire said steam generator. The steam, after use in concentrating and drying the waste sulphite liquor, is then used, at its reduced pressure, to operate the above-mentioned steam consumers of the sulphite pulp plant. By borrowing steam between the plant steam generator and the plant steam consumers, the waste sulphite liquor conversion is accomplished with a minimum of steam loss in evaporation.

The invention will be understood from the following description when considered in connection with the accompanying drawings forming a part thereof and in which:

Fig. l is a diagrammatic view of an arrangement of a portion of the apparatus of the present invention;

Fig. 2 is a continuation of the diagrammatic View shown in Fig. l;

Fig. 3 is a -diagrammatic view of another embodiment of the portion of the invention shown in Fig. 2;

Fig. 4 is a diagrammatic view of an embodiment of the invention wherein waste sulphite liquor is treated Patented July 30, 1957 with steam to prevent scaling of the evaporating apparatus;

Fig. 5 is a view similar to Fig. 4 but of another embodiment of the invention; and

lFig. 6 is -a view similar to Figs. 4 and 5 but of a further embodiment of the invention.

Like characters of reference refer to the same or to similar parts throughout the views.

Referring to Fig. l of the drawings, the reference numeral 10 designates a digester of conventional construction which discharges through the bottom 11 thereof into a pipe 12 communicating with a discharge conduit 13. Steam for heating the contents of the digester to cooking temperature is conducted thereto from a steam generator shown diagrammatically at 14 (Fig. 2) through steam line 15 and pipe 12 While sulphite acid use-d in the digester is introduced at the bottom thereof through pipes 16 and 12. Chips are conducted into the top of the digest er through a conduit 17. l

As is usual in the operation of such a digester, at the start of each batch the digester 10 is loaded with wood chips conducted thereinto through conduit 17 and lled with sulphite acid which enters the digester through pipes 16 and 12. The charge of wood chips and sulphite acid is then cooked by steam conducted to the digester through lines 15 and 12. Upon completion of the cooking operation, the contents are discharged from digester 10 into blow tank 18 through line 12 and discharge con duit 13.

` Gases (SO2) flashed olf during blow-down are vented from blow tank or pit 18 through gas line 19 into a surface condenser 20 wherein vapor in the gas is condensed by flowing in contact with surface cooled by cool waste sulphite liquor collected in a storage tank 21 during operation of the present invention as hereinafter described. The cool waste sulphite liquor is conducted to condenser 20 through line 22 and, after condensing vapor in the SO2 gas and becoming heated by passing in heat exchange relationship with said gas, is passed to the upper part of an absorber 23 through conduit 24. Condensate from y condenser 20 ows to hot wash container 25 through line y by pump 33 from container 25 through lineV 34 into the 26 while the SO2 gas, after the vapor has been removed therefrom is passed to the lower part of absorber 23 through gas line 27. Gases owing into absorber 23 through gas line 27 are absorbed by waste sulphite liquor flowing into the absorber through conduit 24. Any unabsorbed gases are vented to the atmosphere from the absorber through outlet 28. The waste sulphite liquor, after absorbing SO2 in the absorber, flows to blow tank 18 through conduit 29 where it is mixed with the blowndown pulp from digester 10 to reduce the pulp consistency so that the same may be pumped from said tank. The temperature' of the pulp and liquor in blow-tank 18 would normally be approximately 185 F. at which temperature the SO2 therein would remain in solution. l

The solution of pulp and waste sulphite liquor is piunped from blow tank 18 by pump 29' through line 30 into suitable pulp washing apparatus such as rotary vacuum filters 31 and 32 arranged in series. The washing apparatus would normally be designed to wash approximately or more of the waste sulphite liquor from the pulp with a dilution of less than one pound of water per pound of pulp and at the same time discharge liquor at the temperature at which it was received, that is, approximately F. The mixture entering the washing ap-V paratus through conduit 30 is washed with a mixture of received from the evaporating apparatus hereinafter described. The condensate and hot water mixture is pumped washing apparatus. Also hot water from water storage 35, which water is received from evaporating apparatus hereinafter described, is pumped into the washing apparatus by pump 36 through line 37. Washed pulp is removed from the washing apparatus through outlet conduit 37 while hot waste sulphite liquor is passed from washer 31 into hot Waste sulphite accumulator 38 through line 39. Waste sulphite liquor fromV washer 32 is recirculated to the washer through recirculating lines 39 and 40 by recirculating pump 41. To maintain the proper pulp consistency in the washers and also in blow tank 18, a portion of thehot waste sulphite liquor from accumulator 38 is passed to the washers'through line 42 and to the blow tank through lines 42 and 43 by circulating `pump 44. SO2 gas from accumulator 38 is conducted to absorber The stripper evaporator, as shown in Fig. 1, consists of four stages of evaporation indicated at A, B, C, and D. Each stage comprises aflashachamber 48 and a condenser 50 both of which are maintained under vacuum by a steam ejector 51. Cooling medium for condensers 50 of stages A and B is provided from the cool waste sulphite liquor storage tank 21 and flows through said condensers serially, passing into condenser 50 of stage B in line 52. After ilowingthrough condenser 50 of stage B, the waste sulphite liquor flows to condenser 50 of stage A by way of line 53-thereafter passing through said condenser and outwardly therefrom into pipe 54. Condensers 50 of stages D and C are supplied with a water cooling medium which enters condenser 50 of stage D through cool water conduit 60Y and passes through said condensers serially, flowing from condenser 50 of stage D to condenser 50 of stage C through line 61 and from the condenser of stage C into hot water storage 35 through conduit 62. Hot water for use inthe pulp washing apparatus, hereinbefore described, is thusly provided.

From pipe 54, the waste sulphite liquor is passed serially through condensers 55 and 56, said condensers communicating with one another through pipe 57. Waste sulphite liquor from condenser 56 flows to flash chamberv 48 of stage A through conduit 58 while waste sulphite liquor from the hot waste sulphite liquor accumulator 38 flowing through conduit 47 also passes to said flash chamber. The hot waste sulphite liquor from accumulator 38 and from the condensers 50, 55, and 56 is cooled and concentrated by successively flashing it through flash chambers 48 of stages A, B, C and D, the liquid from chamber 48 of stage A flowing therefrom to the flash chamber of stage B through line 59 in which chamber it is flashed and passed to chamber 48 of stage C through conduit 63. In the hash chamber of stage D, the liquor` flowing thereto through line 64 is ashed and the remaining liquid flows to pump 65 through conduit 66 and is pumped to the cool waste sulphite liquor tank 21 through line 67.

The temperature of the waste sulphite liquor flowing u proximately 160 F. The temperatur-eef the waste sulv, phite liquor is progressively reduced by the flash cham-` bers 48,0f stages A, B, C,`and D so that the temperature of the liquor leaving flash chamber 48 of stage D throughr conduit 66 and passing to the cool Waste sulphite Aliquor tank 21 throughline 67 is Vat substantially 100 F.

` heated under pressure.

The vapor flashed olf in ilash chambers 48 flows to the condenser 50 of the stage with which the chamber is associated through a line 68 thereafter to be condensed in said condensers 50. The condensate from condenser 50 of stage A is passed to condenser 50 of stage B through conduit 69 wherein it is ashed and the condensate from condenser 50 of stage B ows to hot wash container 25 through line 70. Condensate produced in condenser 50 of stage C is passed to condenser 50 of stage D through conduit 71 and is flashed in the condenser of stage D. The condensate forminggiu condenser 50 of stage D is passed to hot water storage 35 through line 72. In this manner, the heat contained in the condensate' is recovered and the SO2 gas removed therefrom.

Steam line 15 is connected to each of the ejectors 51 of stages A, B, C, and D through steam conduits 73 and 74, steam conduit 73 being in communication with steam line 15 while conduit 74 is in communication with conduit 73. Ejector 51 of stage D receives steam from conduit 73 while the ejector of stages C, B, and A respectively, receive steam fromv conduit 74. The vapor removed from condenser 50 of stage D by ejector 51 flows through line 75 to condenser 50 of stage C wherein the condensibles are condensed and from which the vapor is withdrawn by ejector 51 for stage C. The vapors removed from the condenser for Vstage C by the ejector therefor are passed to condenser 50 of stage B wherein condensibles are condensed therefrom. Vapor withdrawn by ejector 51 of stage B flows to condenser 50 of stage A through line 77 and the condensible portion thereof is condensed in the condenser 55 through line 78. The non-condensibles from condenser 55, which comprises SO2 gas, is conducted through conduit 78 to the sulphite acid container for the plant, not shown, while condensate from condenser 55 ows through line 79 to condenser 50 of stage A wherein it is dashed. In the present invention, the steam cjectors 51 of stages A, B, C, and D serve a double purpose in that they maintain a vacuum on the ash chambers 48 and condensers 50 of the stage with which they are associated and also build the pressure of SO2 gas back to a desired amount, for example, one pound per square inch gauge. The ejector steam is condensed from the SO2 gas in the various condensers so that a water saturated SO2 gas is released from the stripper evaporator through conduit 78. It will be noted that in accordance with the method and apparatus of the present invention, the waste sulphite liquor flowing to storage tank 21 through line 67 is concentrated without the use of auxiliary heat or excessive heating surfaces and that the SO2 gas is removed therefrom and reclaimed.

As shown in Fig. 2 of the drawings, waste sulphite liquor from storage tank 21 of Fig. 1 is conducted through a conduit 80 to preheating apparatus comprising, as shown, three preheaters 81, 82, and 83. The waste sulphite liquor in line 80 passes to a feed pump 84 which pumps the liquor into preheater 81 through line 85. From preheater 81, the liquor flows either to preheater 82 or to preheater 83 passing to preheater 82 through line 86 which is valved at 87 and 88 or to preheater 83 through line 86 and line 89 which is valved at 90. Heated waste sulphite liquor from preheater 82 passes into conduit 91 through valved line 92 while heated liquor from preheater 83 flows into conduit 91 through valved line 93. From conduit 91, the preheated waste sulphite liquor passes into conduit 94 thence through a circulating pump 95, which places the liquor under pressure into a plurality of heaters 96 through a feed line 97 in which heaters the liquor is Each of the heaters 96 receives feed from line 97 through valved connections 98 and discharges the heated waste sulphite liquor through valved outlet connections 99 into au outlet conduit 100. Heated waste sulphite liquor from the conduit 108 is passed to a steam converter 101. Converter 101 is under such lower pressure than the heaters that the waste sulphite liquor is ashed into steam some of which steam is condensed and the remainder of which is removed from the converter in a vaporous state.

As shown, steam from the converter 101 ows outwardly thereof and into steam line 15 through conduit 102. A portion of the steam in line 102 is passed through conduits 103 and 104 to preheaters 82 and 83. Steam enters preheater 83 through line 104 which line is valved adjacent the preheater while steam ows to preheater 82 through conduit 104 through connection 105 which connection is valved. It will be noted that the Various steam connections and waste sulphite liquor connections to preheaters 82 and 83 are so valved that one of the heaters may be disconnected from the circuit and cleaned without interfering with the functioning of the other preheaters. Heaters 96 receive steam for the heating of the waste sulphite liquor flowing thereinto through lines 97 and 98 from a steam conduit 106 which receives steam from steam line 15, the steam from conduit 106 flowing into said preheaters through valved connections 107. Condensate from heaters 96 passes into a condensate line 108 through Valved connections 109; said condensate thereafter passing to a secondary steam converter v110 which is under such pressure that part of the condensate flashes into steam. Steam from converter 101 also flows into steam converter 110 through lines 102 and 103, and, by heat interchange in secondary converter 110, flashes additional condensate from heaters 96 entering said converter through line 108 into steam. The remaining condensate is returned from converter 110 through line 129 to steam generator 14. Condensate from the preheaters 82 and 83 flows through valved connections 111 into condensate line 112 which is connected to receive condensate from secondary steam converter 110 and connects with a conduit 113 conducting condensate from preheater 81 to a ash chamber 114.

In operation, the waste sulphite liquor flowing into feed pump 84 through conduit 80 is brought up to the operating pressure of steam converter 101 and passed into preheater 81 through line 85. From preheater 81, the waste sulphite liquor is conducted to either or both of the preheaters 82 or 83, and after heating therein is conducted to the heaters 96 through either or both lines 92 and 93 into line 91 and from line 91 through conduit 94, circulating pump 95, and line 97. From line 97, the preheated waste sulphite liquor is conducted to any one or all of the heaters 96 through connections 98. After heating in the heaters 96, the waste sulphite liquor is passed into lines 100 through outlet connections 99 thence into the steam converter 101. It will be noted, that the inlet connections 98 and the outlet connections 99 are so valved that any one or all of the heaters may be used and various heaters may be removed from the line for cleaning as desired. Preheating in the preheaters 81, 82 and 83 and the heating in heaters 96 is done under pressure to avoid steaming in the waste sulphite liquor so as to red uce the scaling on the preheaters and heater surfaces. As shown, the liquid level in steam converter 101 is controlled by capacity control valve 116 in line 91 while the pressure in said steam converter is controlled by pressure control valve 115 in line 100.

After removal of vapor therefrom, in converter 101, a portion of the waste sulphite liquor of the desired concentration' is withdrawn from the bottom of steam converter 101 through outlet conduit 117 controlled by a specic gravity control valve 118 which controls the specific gravity of liquor flowing through outlet line 117. Another portion of the Waste sulphite liquor of the desired concentration ows from the steam converter 101 through line 94, in which it is diluted by waste sulphite liquor enterlng said line through conduit 91, and is thereafter pumped by circulating pump 95 into the heaters 96. The ashing of the waste sulphite liquor in steam converter 101 provides calcium sulphate crystals which have surfaces sufficiently large that the scaling of heaters 96 by said liquor passing thereinto through lines 94, 97 and 9 8 will be reduced. These crystals will have a gentlev scouring action to remove any scale adhering to the tubes and will prevent super-saturation of calcium sulphate in the heater tubes by offering a surface on which the calcium sulphate will tend to first crystallize and will 'prevent super-saturation of calcium sulphate in the steam converter 101.

Concentrated waste sulphite liquor owing from steam converter 101 through line 117 is passed to a dryer 119. As shown in Fig. 2, the dryer 119 comprises a rotating drum 120 across the face of which an even lm of concentrated waste sulphite liquor from line 117 is distributed by distributor 121. Steam from steam converter 101 owing through lines 102 and 103 passes into the drum 120 so as to heat the outer periphery thereof through line 122. The heat of the steam is such that the lm of concentrated waste sulphite liquor will be dried into solid form in one revolution of the drum and the dry solids willv thereafter be removed from said surface bya scraper or other desirable means. The dried solids which comprise finely divided dry crystals somewhat similarrto pulverizer coal are removed from the dryer by a screw conveyor `or rotary air-lock, not shown, and passed into line 122', which, as shown, is connected to burners of steam generator 14. The dryer 119 is so enclosed that the vapor released from the waste sulphite liquor in drying may be conducted through a pipe 123 to preheater 81 and thereby used to preheat waste sulphite liquor owing into said heater. The condensate from the dryer 119 passes into pipe 123 through line 124, and together with the condensate from heater 81, ilows through line 113 into flash chamber 114. The steam from ash chamber 114 ows into condenser 56 (Fig. 1) through conduit 125 while the condensate from said ash chamber is pumped by pump 126 through line 127 into condenser 56. The condensate from condenser 56 flows from condensate line 128 into line 79 which, as heretofore described, extends between condenser 55 and condenser 50 of stage A.

As shown in Fig. 2, steam from steam converter 101 passes through lines 102 and 103 into secondary steam converter 110 from which converter condensate passes into preheaters 82 and 83 through line 113 as hereinbefore described. Condensate from converter 110 also flows to the steam generator 14 through conduit 129. Steam from secondary converter 110 is passed to steam consumers such as paper machines through steam conduit 130.

The waste sulphite liquor from storage 21 may be dried by means of drying apparatus other ythan the drum dryer 119 of Fig. 2. As shown in Fig. 3, waste sulphite liquor from storage tank 21 ows into the suction side of feed pump 84 through line 80 and is fed by said pump through line 85 into a preheater 81'. From preheater 81', the heated waste sulphite liquor is passed through conduit 131 to preheater 132 where it is further heated prior to passage thereof through line 133 into the upper part of a scrubbing tower 134. The scrubbing tower is used to scrub gases entering the lower part thereof by passing the gases which ow upwardly in the towercountercurrent to and in contact with the heated Waste sulphite liquor which passes downwardly in the tower. The scrubbed gases are vented through a vent pipe 135 while the waste sulphite liquor, after use in scrubbing gases, is pumped from the lower portion of tower 134 by pump 136 through line 137 into preheater 81. Preheaters 81, 82 and 83 are arranged slightly diiferently than in Fig. 2 inasmuch as the waste sulphite liquor is heated by the passage thereof serially through the heaters. That is, from the preheater 81, heated waste sulphite liquor passes to heater 82 through line 86 and after the heating thereof in preheater 82 is passed to-preheater 83 through line 92. Waste sulphite liquor heated in the heater 81, 82 and 83 is then passed from heater 83 into line 93 thence into conduit 91. The heating medium for preheaters 81, 81',

82, and 83 is Condensatefrom'secondary steam'converter 110 whiclrcondensateV is passed through the. heaters serially and'enterspreheater 83 throughcondensate line 1'12. Condensate after use in heater 83 is passed to heater 82' through line 92' and'after'use in preheater' 82 is passed topreheater 81 through line `86. The condensate from preheater 81 is conducted to preheater 81' through conduit 138" and'after use in` preheater 81" is conducted-through line 1'11` to hotwash tankV 25 (Fig. 1). The waste sulphite liquor inconduit 91 flows into'c'onduit 94YV and isrpumped'by pump' 95 into line 97 whence it passes into heaters 96, as hereinbefore described in the description of the, embodiment ofthe invention shown in Fig. 2. After heating in heaters 96', the waste sulphite liquor is passed through outlet conduit 100 to the steam converter 101 which converter is'under such pressure that'the waste sulphite liquor is ilashed into steam some ofi-which is condensed andthe remainder of Which'is removed from the` converter as vapor. The operation of theiconverter is the same as in theembodiment of the invention shownv in Fig. v2'. The steam however, passes or preventing formation of scale in'r the heaters'96' and in.t

the converter 101. In the embodiment of the invention illustrated in Fig.'4, fthev waste' sulphite liquor owing steam line through conduit 106. Treatment by steam flowing'to` scrubbing tower 13'4" through lines 131 and 1133. The `condensate from preheater 132 flows into condensate-line 138 between preheaters 81 and 81 through conduit 141; Concentrated waste sulphite liquor from ilashtank- 139'passes linto a spraydryer 142'through outlet conduit 143, conduit 143 being connected to rotary spray head orv atomizert144 revolved at a high speed by a motor 145. The spray from atomizer 144 is dried by fluegases from steam generator 14 which is conducted to the dryer 142 through flue 14'. By drying the waste sulphite liquor in thespray dryer, calcium sulphate solids somewhat similar to pulverized coal are formed, which solids are removed from the drying gases by cyclones 146 inthe dryer 142. The solids after separation from gases pass downwardly and outwardly of the dryer through outlet pipe 147, controlled by an air-lock 148, and into a fuel feed pipe 149. The solids are carried through feed pipev 149 into a steam boiler 14 through a burner 150 in an air stream provided by fan 151.

' Gases separated from solids by the cyclones in dryer 142 are removed by a fan 152 which withdraws said gases from the dryer through outlet pipe 153 and introduces said gases into scrubbing tower 134 through gas inlet 154. As hereinbefore set forth, the gases are scrubbed in tower 134 by passing them countercurrent to and in contact with the waste sulphite liquor flowing into the top of the tower through line 133 and downwardly in thel scrubber. v

While itis highly desirable to flow waste sulphite liquor from accumulator 38 through the multiple stripper evaporators as hereinbefore described, it is possible to obtain a dried solid by conducting hot waste sulphite liquorfrom accumulator 38 to steam converter 101 of Figs. 2 and 3 through conduit 200lindicated by dot and dash lines lines in Figs. l, 2 and 3. Concentrated waste sulphite liquor so conducted to converter 101 would thereafter be dried as hereinbefore set forth in the description of Figs. 2 and 3.

So that the waste sulphite liquor flowing from the preheaters to heaters 96 through lines 91- and, 94 in Figs. 2- and 3 and thence to converter 101 through line100 mayhave a high solution of calcium sulphate therein, it.

may'be desirableto precipitate said calcium sulphate by treating the preheated waste sulphite thereby minimizing' in tank 15S1precipitates the' calcium sulphate in the waste sulphite liquor prior to the passage of said liquor from tank 155 into line 91 thence into conduit 94. Scaling of the heaters 96, only oneY of which is shown in Fig. 4, is thereby greatly minimized or prevented.

The form of the invention shown in Fig.. 5 is somewhat' similar to that shown in Fig. 4, but a further treatment tankis positioned in the line leading from heaters 96 to converter 101. A treatment tank 157 is positioned in outlet conduit so that heated waste sulphite liquor. from heater orheaters 96 flows into said treatment tank which is similar to treatment tank 155. Steam for precipitating calcium sulphate'in the waste sulphite liquor delivered in tank 157 through linev 100 is received by said tank from steam line 15 through lines 106 and 158. After calcium-sulphate is precipitated from the waste sulphite liquorV in'tank 157, the liquor is passed into the upper portion of steam converter 101 through line 100. In the embodiment of the invention shown in Fig. 6, waste sulphite liquor flowing from the preheaters to the heaters 96 through lines 91', 94, 97 and 98 is treated by steam from steam converter 101 to precipitate the calcium sulphate in said liquor. As shown, steam which passes from steam converter 101v through conduit 102 flows tol secondary steam converter through line 103 as hereinbefore set forth in the description of the embodiment of the invention shown in Fig. 2. Some of the steam from Aline 103'is passed through conduit 159 (Fig. 6)- to treatment tankl 155 wherein it is used to precipitate the calcium sulphate in the Waste liquor passed into said treatment tank` through line 91. After treatment, the waste sulphite liquor is passed through lines 91', 94 and pump 95, thence through lines 97 and 98 into heater 96, as set forth in the description relating to the embodiment of the invention shown in Fig. 4. In this manner scaling of the heaters 96, only one of which is shown in Fig. 6 is prevented.

It will be apparent that various modifications may be made in the form of the apparatus herein disclosed and in the steps of the process herein described without departing-from the spirit of the invention which is not t0 be limited excepting by the scope of the appended claims.

What is claimed is:

l. A process of concentrating and drying waste sulphite liquor obtained from a mixture of fibrous material and sulphite cooking liquor which comprises ash evaporating the waste sulphite liquor to concentrate said liquor and liberate SO2 therefrom, feeding concentrated waste sulphite liquor into a heating zone, heating said liquor under a predetermined pressure in said heating zone to prevent steaming thereof, further concentrating said heated liquor by flashing vapor therefrom in a zone of lower pressure than said heated liquor, flowing further concentrated waste sulphite liquor from the zone of lower pressure to a drying zone, and drying further concentrated liquor in the drying zone into solid form.

2. A' process of concentrating and dryingy waste sulphite liquor obtained from a mixture of fibrous material and sulphite cooking liquor flash evaporating said waste. sulphite liquor to concentrate the liquor and liberate SO2 therefrom, feeding concentrated waste sulphite liquor into a heating zone, heating said liquor under apredetermined pressure in said heating zone to pre vent steamingV thereof, further concentrating said heated liquor by flashing. vapor therefrom in a zone of lower pressure than said heated liquor, flowing further concenaporrea trated waste sulphite liquor from the zone of lower pressure to a drying zone, and drying further concentrated liquor in the drying zone in'to solid form by passing the further concentrated waste sulphite liquor and vapor from said zone of lower pressure in indirect heat exchange relationship with one another in said drying zone.

' 3. A process of concentrating and drying waste sulphite liquor obtained from a mixture of fibrous material and sulphite cooking liquor flash evaporating said waste sulphite liquor to concentrate the liquor and liberate SO2 therefrom, feeding concentrated waste sulphite liquor into a treating zone, treating said liquor in the treating zone so as to precipitate calcium sulphate therein, flowing treated liquor from the treating zone into a heating zone, heating said liquor under a predetermined pressure to prevent steaming thereof, further concentrating said heated liquor by flashing vapor therefrom in a zone of lower pressure than said heated liquor, flowing further concentrated waste sulphite liquor from the zone of lower pressure to a drying zone, and drying further concentrated liquor in the drying zone into solid form.

4. A process of concentrating and drying waste sulphite liquor obtained from a mixture of fibrous material and sulphite cooking liquor flash evaporating said waste sulphite liquor to concentrate the liquor and liberate SO2 therefrom, feeding concentrated waste sulphite liquor into a treating zone, treating said liquor in the treating Zone with vapor so as to precipitate calcium sulphate therein, flowing treated liquor from the treating zone into a heating zone, heating said liquor under a predetermined pressure to prevent steaming thereof, further concentrating said heated liquor by flashing vapor therefromV in a zone of lower pressure than said heated liquor, passing vapor flashed from said zone of lower pressure into said treating zone to treat said liquor passed thereinto, flowing further concentrated waste sulphite liquor from the zone of lower pressure to a drying zone, and drying further concentrated liquor in the drying zone into solid form.

i 5. A process of concentrating and drying waste sulphite liquor obtained from a mixture of fibrous material and sulphite cooking liquor flash evaporating said waste sulphite liquor to concentrate the liquor and liberate SO2 therefrom, feeding concentrated waste sulphite liquor into a treating Zone, treating said liquor in the treating Zone so as to precipitate calcium sulphate therein, flowing the treated liquor from the treating zone into a heating zone, heating said liquor under a predetermined pressure to prevent steaming thereof, passing heated liquor from the heating zone into another treating zone, treating saidheated liquor in the other treating zone to precipitate calcium sulphate therein, concentrating said last-mentioned treated liquor by Aflashing vapor therefrom in a zone of lower pressure than said last-mentioned treating zone, flowing further concentrated waste sulphite liquor from the zone of lower pressure to a drying zone, and drying further concentrated'liquor in the drying zone into solid form. v

v6*.*111A the`operation of a sulphite pulp plant having a steam generatorfor supplying steam thereto, and an intermittently operated digester receiving steam from said generator,q`the process of concentrating and drying resdualwaste `sulphite liquor which comprises intermittently dischargingla mixture of pulp and sulphite cooking liquor from the digesting Zone, obtaining residual waste sulphite liquor by separating cooking liquor from said p ulp, concentrating residual waste sulphite liquor, heating concentrated waste sulphite liquor under a predetermined pressure to prevent steaming thereof by steam from said A'Usteam generator, further concentrating the heated liquor by flashing vapor therefrom in a zone of lower pressure than said heated liquor, passing vapor flashedfrom said zone "of lower pressure into the steam from the steam" generator, drying further concentrated concentrating means, waste sulphite conducting means in communication with the separating means so as to receive separated liquor therefrom and in communication with said concentrating means so as to conduct separated liquor thereto, concentrate receiving means, concentrate conducting means communicating with said receiver and with the concentrating means, fluid heating means in communication with the concentrate receiver to receive concentrate therefrom, a flash chamber in communication with the heating means to receive heated concentrate therefrom, said flash chamber being under such lower pressure than the heating means that vapor is flashed from the concentrate, and a dryer in communication with the flash chamber to receive further concentrated waste sulphite liquor therefrom, said dryer comprising a rotatable drum with means for distributing said concentrated waste sulphite liquor in a film on the outer periphery thereof, and means for heating said drum and thereby drying said liquor to solid form.

8. A sulphite pulp plant comprising a digester adapted to receive a fibrous substance, sulphite cooking liquor and steam, means for blowing-down said digester, separating means adapted toseparate fibrous substance and cooking liquor, means for conducting the mixture blowndown from the digester to the separating means, liquid concentrating means, waste sulphite liquor conducting means in communication with the separating means so as to receive separated liquor therefrom and in communication with said concentrating means so as to conduct separated liquor thereto, concentrate receiving means, concentrate conducting means communicating with said receiver and with the concentrating means, fluid heating means in communication with the concentrate receiver to receive concentrate therefrom, a flash chamber in communication with the heating means to receive heated concentrate therefrom, said flash chamber being under such lower pressure than the heating means that vapor is flashed from the concentrate, a dryer, a flue for conducting flue gases from the steam generator into said dryer, an atomizer in the dryer, and a concentrate inlet conduit communicating with the flash chamber and with said atomizer whereby further concentrated waste sulphite liquor is sprayed into the flue gases and solidified.

9. In the operation of a sulphite pulp plant having a steam generator for supplying steam thereto and an intermittently operated digester receiving steam from said generator, the process of concentrating and drying residual waste sulphite ,liquor which comprises intermittently discharging a mixture of pulp and sulphite cooking liquor from the digester, obtaining residual waste sulphite liquor by separating cooking liquor and sulphite pulp, `concentrating residual waste sulphite liquor, preheating concentrated residual waste sulphite liquor in a preheating zone, further heating the preheated liquor by steam from said steam generator under a predetermined pressure to prevent steaming of the liquor, further concentrating said heated liquor by flashing vapor therefrom in a zone of lower pressure than said heated liquor, passing a portion of the vapor flashed from said zone of lower pressure into the steam from the steam generator, passing another portion of the flashed vapor into said preheating zone whereby concentrated residual waste sulphite liquor is preheated, by passing in indirect heat exchange relationship with said vapor, and dryingi said further concentrated liquor into solid form.

:2,so1,1eisA 10. In the operation of a sulphite pulp planthaving a steam generator for supplyingsteam .theretogand ank intermittently operated digester receiving steamfrom said generator, the process of concentrating and drying residual waste sulphite liquor which comprises intermittently discharging a mixture of'pulp and sulphite cooking liquor from the digester, obtaining', residual waste sulphite liquor by separating cooking liquor and said plup, concentrating residual waste sulphite liquor, preheating concentrated waste sulphite liquor in a preheating zone, further heating the preheatedliquor by flowing it in indirect heat exchange relationship with steam from said steam generator, further concentrating4 the heated liquor by flashing vapor therefrom in a zone of lower pressure than said heated liquor, passing a portionof the vapor flashed from said Zone of lower pressure into the steam from the steam generator, flowing another portion of the vapor from said lower pressure zone into the preheating zone. whereby concentrated residual waste sulphite'liquor is preheated by passing in indirect heat exchange relationship with said vapor, flowing a further portion of the vapor from said lower pressure zone and condensate from the heating zone into a steam converting zone wherein said condensate is vaporized, flowing vapor from the steam converting zone to steam consumers of said sulphite pulp plant, and drying further concentrated liquor from the lower pressure zone into solid form by passing the said further concentrated waste sulphite liquor and vapor from said zone of lower pressure in indirect heat exchange relationship with one another in said drying zone.

' 11. In a sulphite pulp plant comprising a steam generator, steam conduit means for conducting steam from the steam generator, a digester adapted to receive a brous substance, sulphite cooking liquor and steam f from the steam generator, means for blowing-down said digester, separating means adapted to separate fibrous substance and cooking liquor, means for conducting the mixture blown down from the digester to the separating means, waste sulphite liquor receiving means, separated waste sulphite liquor conducting means in communication with the separating means so as to receive separated liquor therefrom and in communication with said waste sulphite liquor receiving means so as to conduct separated liquor thereto, heat exch-ange means arranged so that vapor and liquid pass in indirect heat exchange relationship therein to heat said liquid, said heat exchanging means being in communication with said steam conduit means to receive steam therefrom and with the waste sulphite liquor receiving means to receive waste sulphite liquor therefrom, a flash chamber in communication with the heat exchanging means to receive heated liquor therefrom, said flash chamber being under such lower pressure than the heat exchanging means that vapor is flashed from the liquor, a vapor discharge conduit in communication with said steam conduit means and with the flash chamber so as to conduct vapor from the flash chamber to said steam conduit means, -a dryer in communication with the flash chamber to receive concentrated waste sulphite liquor therefrom, said dryer being adapted to dry moisture from said liquor and produce solids therefrom, a secondary steam converter in communication with said flash chamber so as to receive vapor therefrom, a condensate line between the secondary steam converter and said heat exchanging means through which the condensate flows to said secondary steam converter, said secondary steam converter being so arranged that the condensate is vaporized therein, a steam consumer conduit for withdrawing steam from said secondary steam converter for use in said sulphite pulp plant, and a condensate feed line between the secondary steam converter and thev steam generator.

and steam, means for blowing-down said digester, separating means adapted to separate fibrous substance and cooking liquor, means for conducting the mixture blowndown from the digester to the separating means, liquor concentrating means, waste sulphite liquor conducting eans in communication with the separating means so as to`receive separated liquor therefrom and in communication with said concentrating meansso as to conduct separated liquor thereto, concentrate receiving means, concentrate conducting means communicating with said receiver and with the concentrating means, fluid heating means in communication with the concentrate receiver to receive concentrate therefrom, a treating tank communicating with` said fluid heating means to receive concentrate and connected to receive steam to precipitate calcium sulphate in the liquor, a flash chamber in communication with the treating tank to receive treated concentrate therefrom, said flashing chamber being under such lower pressure than the heating means that vapor is flashed from the concentrate, and a dryer in communication with the flash chamber to receive further concentrated waste sulphite liquor therefrom, said drier being ladapted to dry moisture from said liquor and produce solids therefrom.

13. A sulphite pulp plant comprising a digester adapted to receive a fibrous substance, sulphite cooking liquor and steam, means for blowing-down said digester, separating means adapted to separate fibrous substance and cooking liquor, means for conducting the mixture blown-down from the digester to the separating means, liquor concentrating means, waste sulphite liquor conducting means in communication with the separating means so as to receive separated liquor therefrom and in communication with said concentrating means so as to conduct separated liquor thereto, concentrate receiving means, concentrate conducting means communicating with said receiver and with the concentrating means, a treating tank communicating with said concentrate receiver to receive concentrated liquor therefrom and connected to receive steam to precipitate calcium sulphate in the liquor, fluid heating means in communication with the treating tank to receive treated concentrate therefrom, another treating tank communicating with said heating means to receive heated concentrated liquor therefrom and connected to receive steam to further precipitate calcium sulphate in the concentrated liquor, a flash chamber-in communication with said other treating tank to receive treated liquor therefrom, said flashy adapted to dry moisture from said liquor and produce solids therefrom.

References Cited in the le of this patent UNITED STATES PATENTS 1,103,216 Moore et al. July 14, 1914 1,218,638 Fest Mar. 13, 1917 1,263,486 Thorne Apr. 23, 1918 `1,308,184 McAfee July 1, 1919 1,469,958 Richter Oct. 9, 1923 1,864,619 v Richter June 28, 1932 2,025,891 Paulson Dec. 31, 1935 2,108,567 Scholler et al. Feb. 15, 1938 2,197,059 Seidel Apr. 16, 1940 2,238,456 Tomlinson Apr. 15, 1941 2,352,304 Young June 27, 1944 2,385,955 Tomlinson Oct. 2, 1945 2,494,098 Lockman Ian. 10, 1950 2,574,193 .Savell Nov.'6, 1951 2,676,883 Goddard Apr. 27, 1954 

1. A PROCESS OF CONCENTRATING AND DRYING WASTED SULPHITE LIQUOR OBTAINED FROM A MIXTURE OF FIBROUS MATERIAL AND SULPHITE COOKING LIQUOR WHICH COMPRISES FLASH EVAPORATING THE WASTE SULPHITE LIQUOR TO CONCENTRATE SAID LIQUOR AND LIBERATE SO2 THEREFROM, FEEDING CONCENTRATED WASTE SULPHITE LIQUOR INTO A HEATING ZONE, HEATING SAID LIQUOR UNDER A PREDETERMINED PRESSURE THAN SAID HEATING ZONE TO PREVENT STEAMING THEREOF FURTHER CONCENTRATING SAID HEATED LIQUOR BY FLASHING VAPOR THEREFROM IN A ZONE OF LOWER PRESSURE THAN SAID HEATED LIQUOR, FLOWING FURTHERR CONCENTRATED WASTE SULPHITE LIQUOR FROM THE ZONE OF LOWER PRESSURE TO A DRYING ZONE, AND DRYING FURTHER CONCENTRATED LIQUOR IN THE DRYING ZONE INTO SOLID FORM 